Current NASA DSN tasking

My visualisation of current NASA Deep Space Network tasking as per eyes.nasa.gov/dsn (click image to zoom). Several Mars orbiters are lending a hand to transfer Perseverance imagery from the Martian surface, while other space science is going on as normal.

The chart is for 2 PM Australian time, with the Sun overhead in Tidbinbilla, Australia, and Mars overhead in the 7 PM evening sky in Goldstone, California. The respective skies looked like this (click to zoom):

Later in the afternoon, as Mars rose in the sky, Tidbinbilla began to share the load of Martian traffic. As Jupiter and the Sun rose over Madrid, MDSCC prepared to take over traffic from Juno.


A planetary conjunction and a Christmas greeting

It’s time for a Christmas blog post, and there’s really only one thing to write about. On 21 December, there will be a great conjunction, in which Jupiter and Saturn will appear very close together in the early evening sky. Look for them near the western horizon, as they get closer and closer over the next two weeks. The diagram below (from fourmilab.ch) shows what the solar system will look like at conjunction. A line from Earth to Jupiter continues on to Saturn, but skims by the Sun (which is why the “kissing planets” are only visible in the early evening). These two giant planets have not appeared so close for several centuries.

The Christmas connection relates to the Magi mentioned in the Bible: “After Jesus was born in Bethlehem in Judea, during the time of King Herod, Magi from the east came to Jerusalem and asked, ‘Where is the one who has been born king of the Jews? We saw his star when it rose and have come to worship him.’” (Matthew 2:1–2, NIV)

One theory as to what the Magi might have seen was a set of similar conjunctions of Jupiter and Saturn in 7 BC (the great astronomer Johannes Kepler was the first to suggest this – and yes, thanks to a calendrical error 500 years later, Jesus was born around 7–4 BC). There were three such conjunctions in 7 BC: in May, in late September, and again in December. Here is a view of the September one, as seen from Ctesiphon in Parthia (from fourmilab.ch again). The planets Jupiter (♃) and Saturn (♄) would have risen just before sunset, and been visible in the evening twilight (and then throughout the night):

The Babylonians and Persians had an elaborate system of seeing omens in the sky. For example: “If Jupiter becomes steady in the morning: enemy kings will be reconciled. … If Jupiter passes Regulus and gets ahead of it, and afterwards Regulus, which it passed and got ahead of, stays with it in its setting, someone will rise, kill the king, and seize the throne.” So a conjunction is the sort of thing that would have gotten the attention of star-gazers in the Parthian Empire (the planet Jupiter was associated with the god Marduk and with kingship). Others have suggested a nova recorded in China in March of 5 BC. Yet others have suggested that a sequence of astronomical events led the star-gazers to search for a newborn king specifically in the frontier province of Judaea:

Countless paintings show the journey of the Magi across the desert (the one above is from James Tissot). If they were sensible, they would likely have travelled along the trade routes via Palmyra and Damascus. “A cold coming we had of it” wrote the poet T.S. Eliot (adapting lines from a 1622 homily by Lancelot Andrewes), “Just the worst time of the year / For a journey, and such a long journey.”

The real danger was Herod, of course. He had murdered his own sons Alexander and Aristobulus in 7 BC (and was to murder a third son, Antipater, in 4 BC). According to Macrobius (Saturnalia Book 2, IV, 11), Caesar Augustus had quipped “Better to be Herod’s swine [Greek hus] than his son [huios],” making a Greek pun referencing Herod’s Jewish religion and its prohibition on pork. Naturally, a man like that would be less than thrilled at the suggestion that another heir to the throne might exist:

When King Herod heard this he was disturbed, and all Jerusalem with him. When he had called together all the people’s chief priests and teachers of the law, he asked them where the Messiah was to be born. ‘In Bethlehem in Judea,’ they replied, ‘for this is what the prophet has written:

“But you, Bethlehem, in the land of Judah,
are by no means least among the rulers of Judah;
for out of you will come a ruler
who will shepherd my people Israel.”’
[a summary of Micah 5:2–5]

Then Herod called the Magi secretly and found out from them the exact time the star had appeared. He sent them to Bethlehem and said, ‘Go and search carefully for the child. As soon as you find him, report to me, so that I too may go and worship him.’” (Matthew 2:3–8, NIV)

This is the kind of trouble you get when you mix star-gazing boffins and international diplomacy (I have been to enough international scientific events to know how that works). The gospel account makes a further confusing reference to the “star” and mentions the famous gifts of “gold, as to a king; myrrh, as to one who was mortal; and incense, as to a God”:

After they had heard the king, they went on their way, and the star they had seen when it rose went ahead of them until it stopped over the place where the child was. When they saw the star, they were overjoyed. On coming to the house, they saw the child with his mother Mary, and they bowed down and worshiped him. Then they opened their treasures and presented him with gifts of gold, frankincense and myrrh. And having been warned in a dream not to go back to Herod, they returned to their country by another route.

When they had gone, an angel of the Lord appeared to Joseph in a dream. ‘Get up,’ he said, ‘take the child and his mother and escape to Egypt. Stay there until I tell you, for Herod is going to search for the child to kill him.’” (Matthew 2:9–13, NIV)

This “Flight into Egypt” has been a common subject of Christian art. The painting above, by Adam Elsheimer (1609), includes a beautifully painted Milky Way.

Egypt, of course, was a logical destination. We know first-century Alexandria primarily as the scientific and mathematical centre of the world of that time, but it also had a thriving Jewish community, with hundreds of thousands of Jews living in the city, and hundreds of thousands more in the rest of Egypt. The Hellenistic Jewish philosopher Philo was still a boy at this time, as was the Greek scientist Heron, but the Musaeum was fully active. Eventually, Alexandria was also to become one of the most important Christian cities, and the statement “gold, as to a king; myrrh, as to one who was mortal; and incense, as to a God” was from Alexandria. An active Coptic Church is still there (though suffering hardship).

But troubled as the world of 2020 may be, let me wish all my readers a Merry Christmas, and a better 2021!


Spaceprobes in the Solar System

The diagram above (click to zoom) and list below show currently active spacecraft in the Solar System, not including those operating close to the Earth (and I’ve probably missed a few):

  • Voyager 1 and Voyager 2, launched in 1977, now heading into the darkness and still reporting back, even though they are over 17 billion km or 16 light-hours away (not shown above).
  • Cassini–Huygens, launched in 1997, now in the final stages of its exploration of Saturn (see fact sheet).
  • 2001 Mars Odyssey, launched in 2001, and still orbiting Mars.
  • New Horizons, launched in 2006, now en route from Pluto to the Kuiper belt object 2014 MU69, which it should reach in January 2019.
  • Dawn, launched in 2007, currently orbiting Ceres (image shown above the Earth).
  • Akatsuki, launched in 2010, currently orbiting Venus, which it will do until 2018.
  • Juno, launched in 2011, currently orbiting Jupiter, which it will do until February 2018.
  • Hayabusa 2, launched in 2014, currently en route to asteroid 162173 Ryugu, which it should reach in 2018. It will then take a sample which should arrive back home in 2020 (not shown above).
  • ExoMars Trace Gas Orbiter, launched in 2016, currently orbiting Mars and mapping the Martian atmosphere (the associated Mars lander was lost in 2016).
  • OSIRIS-REx, launched in 2016, currently en route to asteroid 101955 Bennu, which it should reach in 2018. It will then take a sample which should arrive back home in 2023 (image shown below the Earth).

In addition to the above, BepiColombo is scheduled to launch for Mercury in October 2018, and SolO is scheduled to launch for the Sun that same month. Also, InSight is scheduled to launch for Mars in May 2018, and Solar Probe Plus is scheduled to launch for the Sun in August 2018.


Metallic hydrogen

It has long been known that hydrogen forms a metallic solid at moderate to low temperatures and extremely high pressures. Last year, Ranga Dias and Isaac F. Silvera at Harvard University were the first to actually produce this metal, using the enormous pressure of 495 gigapascals (see their paper).

At higher temperatures, hydrogen forms a metallic liquid, and this is believed to exist at the heart of Jupiter and Saturn. This liquid has yet to be observed.


Looking back: 2000

As the year 2000 opened, I was in Sydney, watching the New Year’s Eve fireworks. After all the hype about the Y2K problem, I was half-expecting the lights to go out. They did not, of course. Later in the year, the 2000 Summer Olympics were held in Sydney, and the city put on another spectacular show for that:

Also in 2000, genome-sequencing of the plant Arabidopsis thaliana (below) was completed, and described in Nature. The genome is available at arabidopsis.org.

The Cassini probe flew past Jupiter at the end of the year (en route to Saturn), and took some spectacular pictures, including this one of Io in front of the planet:

Films of 2000 included Chicken Run, Chocolat, Gladiator, Pitch Black, Proof of Life, The 6th Day, Thirteen Days, X-Men, and the excellent O Brother, Where Art Thou?.

In books, Ross King published a wonderful little book about Brunelleschi, Dan Brown published the wildly inaccurate Angels & Demons, Umberto Eco published Baudolino (in Italian), J.K. Rowling published the 4th Harry Potter book, and Patricia McKillip published the beautifully oneiric The Tower at Stony Wood.

In music, Britney Spears was still wildly popular. In architecture, the Cathedral of Christ the Saviour in Moscow was rebuilt, and the Tate Modern in London opened. The London Millennium Bridge was closed two days after opening because of resonance problems, which required the retrofitting of fluid-viscous and tuned-mass dampers. Software is not the only thing with bugs.


Juno arrives!

The Juno spaceprobe (above) is just an hour away from orbit insertion around Jupiter. Juno has been in transit, waiting for this day, for almost five years. Juno is solar-powered, with huge 9-metre-long solar panels, to compensate for the fact that the intensity of sunlight around Jupiter is only 4% of what it is here.

Follow the spaceprobe on Twitter or watch the live NASA feed (which is starting now).

Update 1: Juno is into its orbit insertion burn, screaming past Jupiter at a distance of 5,000 km and a velocity of 208,000 km/hr.
Update 2: Engine off. “Juno, welcome to Jupiter!” (NASA/JPL clapping)


Arriving at Jupiter

The Juno spaceprobe (above) is a few days from reaching Jupiter, and beginning its mission of studying that giant planet. Juno has been in transit for almost five years, as shown below:

Juno is now just under 4 million kilometres away from Jupiter. She will spend more than a year examining Jupiter in detail, and will then deorbit, carrying a plaque in honour of Galileo, who discovered that there were moons orbiting that planet.

As seems to be the norm nowadays, the spaceprobe has a Twitter feed for staying in touch. There will certainly be some interesting stories and pictures to come!


Venus and Jupiter in conjunction

The planets Venus and Jupiter were in conjunction last night, as the photograph above (by Neal Simpson) shows. The diagram below (by the Fourmilab) shows why: although Venus is much closer to Earth (and thus much brighter), the three planets are almost in a straight line. Venus and Jupiter should still be pretty close in the sky for the next few nights.

Jupiter in motion

The image of Jupiter above (click for OGG video) was taken in 1979 by Voyager 1. The turbulent rotating cloud bands are clearly visible. The short YouTube video below is the result of Björn Jónsson’s reprocessing of that Voyager 1 data, combining images taken through different colour filters, and holding the Great Red Spot steady. Ian Regan interpolated additional frames for smoothness. This wonderful video highlights the stability of that gigantic storm, which is several times larger than the Earth:

The video is sped up by a factor of about 36,000. See here for more information.